Plants have developed fascinating mechanisms to create ultra fast movements
that often reach the upper limit allowed by physical laws. Inspiration for
new technologies is one of the reasons for the strong interest for these
mechanisms, along with the deep interest of understanding complex, natural
systems. The fern sporangium is a capsule that contains the spores, it is
surrounded by a row of cells called the annulus which acts as a beam. Due to
the water evaporation from its cells, the annulus bends strongly and induces
elastic energy storage during an opening phase. The tension in the cells
breaks when cavitation bubbles appear in the cells, leading to a fast
release of the elastic energy. The fern sporangium then acts as a catapult
which ejects rapidly its spores by closing back to the initial closed shape.
We have analyzed the slow opening motion and the fast catapulting mechanism.
We found that the catapult motion involves two time scales, showing a very
original behavior. In man-made catapults, the recoil motion needs to be
arrested by a cross bar so that the projectile is released from the arm. We
show here that the fern sporangium replaces the essential cross bar by an
elegant poroelastic damping, leading to a completely autonomous, efficient
device.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.MAR.Z40.12